The present invention relates to a biomass resin composition and a process for preparing the same. Also, the present invention relates to a curable resin composition derived from biomass, a molding material of thermosetting biomass resin and a molded article of thermosetting biomass resin, comprising the biomass resin composition. The curable resin composition derived from biomass of the present invention has a low melting point and favorable moldability and the molded article obtained therefrom is excellent in flexibility, impact strength and water resistance. The curable resin composition is particularly suitable as a binder for various organic and inorganic substrates, varnish for impregnating and resin for molding material.
Phenol resin is inexpensive and has excellent properties such as moldability, mechanical properties, heat resistance, electric insulating properties and chemical resistance. Therefore, phenol resin is widely used industrially, as resin for various molding materials, electric parts, mechanical parts, laminating materials, coating materials, abrasives and friction materials.
Phenol resin is usually prepared from the reaction of a phenol and a formaldehyde in the presence of an acid or an alkali catalyst. In the case of a novolak-type, hexamethylenetetramine is usually used together when curing and by heating, an insoluble and infusible curable resin can be obtained. In the case of a resol-type, curing is usually conducted by heating without a curing agent, as a resol-type resin has self-curing properties. It is known that by reacting a phenol with wood flour instead of a formaldehyde, a resin can be obtained, that can be cured by hexamethylenetetramine in the same manner as novolak-type phenol resin. When preparing this resin, abundantly available scrap wood is used and a formaldehyde does not need to be used. Also, the amount of phenol that is used can be reduced significantly. Therefore, this method is extremely significant in terms of environment and resources. As the reaction method of this process, known are the method of reacting at a high temperature without a catalyst (see for example JP-A-61-261358, JP-A-3-59035 and JP-A-3-126728) and the method of reacting in the presence of an acid catalyst (see for example JP-B-61-2697 and Japanese Patent Application No. 175758/1990).
The method of reacting at a high temperature without a catalyst is unfavorable in terms of facilities, as a pressure-resistant reaction apparatus must be used. Also, the yield of resin of the product is low because thermal decomposition of wood tends to occur during the reaction and also, reactivity as raw material for resin is low. On the other hand, in the method of reacting in the presence of an acid catalyst, solvolysis of the wood and reaction between the wood component and the phenol mainly occur due to action of the catalyst and a resin product having high reactivity can be obtained by introducing a phenol nucleus. Therefore, a great deal of research has been conducted regarding the acid catalyst method.
However, the resin composition obtained by chemical reaction of wood and a phenol (phenolization of wood) (hereinafter also referred to as wood resin) usually has a high melting point of 120 to 150° C., after removing excessive unreacted phenols, and is significantly inferior to the conventional novolak resin (melting point 60 to 110° C.) in view of workability and moldability. Also, in wood resin having a melting point of 120° C. or higher, the melting point is close to the usual temperature of crosslinking reaction by a curing agent (hexamethylenetetramine) and therefore, when mold processing, the crosslinking reaction starts before the resin has sufficient flowability. As a result, the curing reaction tends to be inhomogeneous and defects such as voids and air bubbles are formed inside the molded article. Consequently, the obtained molded article is inferior to commercially available novolak resin, in view of mechanical strength and solvent resistance. Furthermore, because the melting point of wood resin is high, the steps of purifying, transferring, discharging and maintenance of facilities are difficult to conduct when preparing the resin.
Also, due to influence of the hydrophilic properties inherent in biomass such as wood, the obtained wood resin and the cured product have strong water absorbing properties and water resistance of products such as a molded article is poor. Products such as a molded article prepared from phenol/wood resin is more fragile than the conventional synthetic phenol/formaldehyde resin and flexibility and impact strength are low.
In order to lower the melting point of wood resin, suggested is the method of leaving part of the unreacted phenol, which is remnant in the reaction product, in the resin as a plasticizer, after phenolization reaction of wood (see for example JP-A-3-328078). According to this method, the softening point becomes low and properties as resin for molding material improves to an extent. However, the gel time is fast by influence of the unreacted phenol and the effect of improving moldability is limited. Furthermore, unreacted phenol, which is present in the resin in a large amount, is unfavorable from the viewpoint of adverse effects to the health of the workers and to the environment.
JP-A-6-192357 discloses the method of lowering the melting point of wood resin by containing phenol in an extremely large amount of 50 times the wood, when reacting wood and phenol. According to this method, the melting point of wood resin can be lowered to at most 100° C. However, because an extremely large amount of phenol is used for the reaction, the yield of wood resin, which is the product, based on the total amount of reacted matter is low and efficiency of the reaction facilities is poor. Also, a great deal of time and energy is necessary to remove the large amount of unreacted phenol after the reaction and therefore, the wood resin is high in cost and low in practicability. The above methods are effective to a certain degree in lowering the melting point of resin, but cannot improve water resistance and flexibility of wood resin.
Consequently, conventional wood resin has the problems that preparation is difficult, melting point is high and moldability and properties are unsatisfactory, thereby being impractical.
The present invention aims to provide a biomass resin composition, wherein the melting point can be controlled freely and which is excellent in flowability, processability and properties after curing and is prepared by a simple process, and a process for preparing the same. Also, the present invention aims to provide a curable biomass resin composition, a binder, a molding material of thermosetting biomass resin comprising the biomass resin composition and a molded article comprising the binder or the molding material of thermosetting biomass resin.